1. Technical Field
The present invention relates to an image bearing member (photoreceptor), a manufacturing method of the image bearing member, an image forming method, an image forming apparatus, and a process cartridge.
2. Background Art
Organic photoconductors (OPC) (photoreceptors) have good properties and have been used in place of inorganic photoreceptors in photocopiers, facsimile machines, laser printers, and multi-functional devices thereof in light of various advantages. Specific advantages for this supersession include, for example, (1) good optical characteristics, for example, a broad range of optical absorption wavelengths and a large amount of light absorption; (2) superior electrical characteristics, for example, high sensitivity and stable chargeability; (3) a wide selection of materials; (4) ease of manufacturing; (5) low cost; and (6) non-toxicity.
However, such an organic photoconductor is soft in general because the charge transport layer therein contains a low molecular weight charge transport material, an inert polymer, etc. as its main component. For this reason, the organic photoconductor involves problems about abrasion resistance, durability to damage, etc., because of the mechanical stress applied to the photoconductor by a development system or a cleaning system during repetitive use in a long period of time in the electrophotography system. Such abrasion and damage of the image bearing member lead to degradation of electric characteristics such as sensitivity and chargeability, resulting in production of defective images with low image density, background fouling, etc. Local damage to a photoreceptor caused by the abrasion involves problems of production of defective images with streaks ascribable to bad cleaning performance for the photoreceptor.
For example, JP-2000-066425-A, JP-2000-171990, JP-2003-186223-A, JP-2007-293197-A, JP-2008-299327-A, JP-4262061-B1 (JP-2004-184991-A), JP-2006-251771-A, JP-2009-229549-A, and JP-2006-084711-A disclose organic photoconductors having charge transport layers containing three-dimensionally cross-linked polymers to improve the mechanical durability of the organic photoconductors.
JP-2000-066425-A mentioned above discloses a charge transport layer containing a three-dimensionally cross-linked polymer formed by radically-polymerizing hole carrier transport compounds having two or more chain-rectionally polymerizable functional group in a molecule by exposure to ultraviolet ray or electron beam. However, this requires elaborate irradiation devices for ultraviolet ray or electron beam, which is a disadvantage in terms of productivity. In addition, charge transport compounds are degraded by ultraviolet ray or electron beam, which leads to deterioration of voltage properties of a photoreceptor.
JP-2000-171990, JP-2003-186223-A, JP-2007-293197-A, JP-2008-299327-A, JP-4262061-B1 (JP-A), JP-2006-251771-A, and JP-2009-229549-A mentioned above disclose charge transport layers containing three-dimensionally cross-linked polymers formed by using charge transport compounds having polar groups such as hydroxyl groups. Although these are successful to some degrees, the charging level lowers because such polar groups remain in the three-dimensionally cross-linked polymers. In addition, the image density tends to deteriorate in high temperature and humidity environment or due to exposure to NOx gases produced by a charger.
JP-2006-084711-A mentioned above discloses a charge transport layer containing a compound in which a polar group such as hydroxyl group of a charge transport compound is blocked and a three-dimensionally cross-linked polymer formed by curing a reaction active species such as melamine.
In this case, although it is possible to prevent such polar groups from remaining in the charge transport layer, the blocked polar group and the reactive activated species tend not to react easily. Therefore, the mechanical durability of the thus-formed layer is inferior.
As described above, in order to improve the mechanical durability of an organic photoconductor, providing a charge transport layer containing a three-dimensionally cross-linked polymer to an organic photoconductor have been intensively investigated. On the other hand, abrasion of a cleaning blade that contacts an organic photoconductor relatively arises as a large problem as the abrasion resistance of the organic photoconductor increases. This creates a new problem of a short working life of a cleaning blade. For this reason, the working life of a process cartridge having an organic photoconductor and a cleaning blade is not prolonged substantially because the durability of the cleaning blade is worsened while the mechanical strength of the organic photoconductor ameliorates.
In addition, in an attempt to improve the cleanability, a lubricant is applied to an organic photoconductor to reduce friction between the organic photoconductor and the cleaning blade. This is successful to some degree but the abrasion of a cleaning blade is not completely prevented.
A charge transport layer having a three-dimensionally cross-linked polymer is generally hard but mostly a cleaning blade is formed of urethane rubber, meaning it is relatively soft. For this reason, when particles such as silica having a grinding feature are contained in toner and frictioned between the photoreceptor and the cleaning blade, the cleaning blade tends to be scraped more and more as the organic photoconductor is less scraped. To decrease the hardness of a charge transport layer having a three dimensionally cross-linked polymer, for example, monomers to soften the charge transport layer, a non-reactive plasticizer, etc. can be copolymerized or mixed. However, adding such a material even in a few amount leads to a substantial degradation of the abrasion resistance of a typical charge transport layer containing a three dimensionally cross-linked polymer. That is, the trade-off between the organic photoconductor and the cleaning blade is not overcome. The mechanism is inferred as follows: Such a non-reactive plasticizer mixed with has poor compatibility so that it is not possible to form a uniform three-dimensionally cross-linked polymer, thereby inhibiting curing reaction, resulting in a significant degradation of mechanical durability. Copolymerization of a monomer to soften a charge transport layer leads to reduction of the cross-linking density of matrix, which directly degrades abrasion resistance.
For that reason, a photoreceptor that has excellent mechanical durability and can reduce abrasion of a cleaning blade that contacts the photoreceptor and a manufacturing method thereof are in demand. An image forming apparatus, an image forming method, and a process cartridge that are able to stably produce quality images over the entire process with a long working life have not appeared on market yet. Development thereof is in strong demand.